The end of the reproductive years of a person's life can often be accompanied by uncomfortable and disruptive symptoms, one of the most common of which is hot flushes. Perimenopause, or premenopause, is the period of years in which normal ovulatory cycles give way to cessation of menses. This time is marked by irregular menstrual cycles. Cycle length begins to increase, and ovulation and fertility decrease. Menopause is typically defined as the point, after the loss of ovarian activity, when permanent cessation of menstruation occurs. In addition, estrogens are involved in various other physiological processes such as the modulation of the immune response and development of cancer (breast, endometrium, colon, prostate). ERα has been proven to be implicated in several diseases, such as breast cancer, and osteoporosis.
It is well established that estrogens play an important role in the development and homeostasis of the reproductive, central nervous, skeletal and cardiovascular systems in both males and females. To date, a plethora of estrogen receptors have been discovered in the brain, involved in various processes such as mood, temperature regulation, sleep, susceptibility to seizure, pain mechanism, and cognitive functions (Toran-Allerand, Endocrinology, 2004, 145, 1069-1074).
Currently, the estrogen receptor (ER) is a nuclear receptor with two known different subtypes. A new subtype ERβ, different from the known ERα subtype (Green, Nature, 1986, 320, 134-139), was recently discovered (Mosselman et al, FEBS Letters, 1996, 392, 49-53). These subtypes have different biological roles and may have selective and effective clinical uses (Harris H. A., Endocrinology, 2002, 143, 11, 4172-4177). ER subtypes share about 50% identity in the ligand-binding domain (Kuiper et al, Endocrinology, 1998, 139(10), 4252-4263), they have similar Estradiol (E2) binding affinities and can hetero- or homodimerize (Cowley, J Biol Chem, 1997, 272, 19858-19862) to form a signalling complex (Kuiper et al, Endocrinology, 1997, 138(10), 863-870; Kuiper, Proc. Natl. Acad. Sci. USA, 1996, 93, 5925-5930). ERβ is strongly expressed in a number of tissues including prostate epithelium (Weihua Z, Proc. Natl. Acad. Sci. USA, 2001, 98, 6330-6335), sympathetic ganglia (Zoubina E. V., J. Urol., 2003, 169, 382-385), colon (Witte D., Hum. Pathol., 2001, 32, 940-944), bladder, ovarian granulosa cells (Nilsson S., Physiol. Rev., 2001, 81, 1535-1565), bone marrow (Shim G. J., Proc. Natl. Acad. Sci. USA, 2003, 100, 6694-6699), breast stroma (Cunha G. R., J. Mammary Gland Biol. Neoplasia, 1997, 2, 393-402), lung, intestine, vascular endothelium, dorsal raphe, parts of the brain (Mitra S. W., Endocrinology, 2003, 144, 2055-2067, Krel W., Proc. Natl. Acad. Sci. USA, 2001, 98, 12278-12282). ERα is expressed in breast epithelium (Palmieri C., Endocr. Relat. Cancer, 2002, 9, 1-13), uterus, bone, ovary theca cells (Couse J., Endocr. Rev., 1999, 20, 358-417), prostate stroma (Chu S., Mol. Cell Endocrinol., 1997, 132, 195-199), liver, testis. The finding of compounds with a specific affinity for one or the other subtypes could provide a selective treatment of estrogen-related diseases such as Alzheimer's disease, menopausal complaints (e.g. hot flushes, vaginal dryness, atrophy), cognitive functions (e.g. anxiety, depression, dementia), osteoporosis, estrogen dependent tumours (uterine, breast, colon, or prostate cancers), benign prostatic hyperplasia, bladder control, hearing disorders, stroke, leukaemia, hypertension, obesity, irritable bowel syndrome, or reproductive aspects such as contraception or infertility. ERβ-selective ligands may be therapeutically useful agents to treat chronic intestinal and joint inflammation (Harris et coll., Endocrinology, 2003, 144, 4241-4249).
According to Warembourg M and Leroy D (Brain Res., 2004, 26; 55-66), ERβ was only detected within the rat dorsal raphe nucleus. In contrast, only ERα-immunoreactivity was seen in the septum, and in the magnocellular supraoptic, paraventricular, arcuate, and premammillary nuclei. These observations provide evidence of a distinct neuroanatomical pattern for the two subtypes of the ERs. Localisation of ERβ in serotonin cells show the link between ERβ and the serotoninergic pathway. Finally, Cyr M et al. described (J Psychiatry Neurosci., 2002, 27, 12-27) the effect of a selective estrogen receptor modulator (SERM) such as raloxifen on 5-HT2a receptor.
In conclusion it seems to be relevant to develop ERβ modulators as compounds of interest in the field of schizophrenia, neurodegenerative diseases such a Alzheimer's disease or Parkinson's disease. For the same reasons, ERβ modulators should be of interest as neuroprotective, antidepressant or anxiolytic agents.
However, the two receptors which act as ligand activated transcription factors, were found in a variety of tissues, and differed in their binding pocket only by two amino acids: Leu and Met in ERα, Met and Ile in ERβ. Those similarities could explain that the control of the subtype alpha or beta led to the same pharmacological effect, as it is the case in preclinical model of hot flush phenomena. While ERα modulator decreased the occurrence of hot flushes in a rat preclinical model (Harris et al., Endocrinology, 2002, 143, 4172-4177), selective estrogen receptor modulators such as spiroindene compounds, which were affine for both subtypes, had the same effect on hot flushes (Watanabe et al., J Med Chem, 2003, 46, 3961-3964).
It has also been shown that estrogen receptors can suppress NFKB-mediated transcription in both a ligand-dependent and independent manner (Quaedackers, et al., Endocrinology 2001, 142: 1156-1166; Bhat, et al., Journal of Steroid Biochemistry & Molecular Biology 1998, 67: 233-240; Pelzer, et al., Biochemical & Biophysical Research Communications 2001, 286: 1153-7). These data show the link between selective estrogen receptor modulators and NFKB which is implicated in apoptosis and immune/inflammatory response.
Many compounds have been described as estrogen receptor agonists or antagonists as they respectively had a similar activity or blocked the activity of estradiol. Such agonist compounds could be used as contraceptive agents in premenopausal women. Antagonists are widely used therapeutic agents in the treatment of breast cancer (Vogel, Anticancer Drugs, 2003, 14, 265-273) whereas agonists are used in HRT (Hormone Replacement Therapy) in post menauposal women (Burkman, Minerva Ginecol, 2003, 55, 107-116) to treat hot flushes, vaginal atrophy. SERMs are compounds that present mixed activities depending on the tissue (McDonnell, J Soc Gynecol Invest, 2000, 7, S10-S15). SERMs might have utility for the treatment of osteoporosis, cardiovascular diseases and related estrogen receptor diseases.
Estrogen receptors adopt different conformations when binding ligands. Three-dimensional structures of ERα and ERβ have been solved by co-crystallisation with various ligands (Pike A. C. W., EMBO J, 1999, 18, 4608-4618; Shiau A. K., Cell, 1998, 95, 927-937). Each ligand influences receptor ERα or ERβ conformations, leading to distinct biological activities.
Various compounds presented as estrogenic agents have been described in US 2003/0207927 A1 and US 2003/0171412 A1. Indazole derivatives presented as potassium channel blockers are described in WO 2004/043354 and WO 2004/043933. The synthesis of various isoxazoles is described in Ind J Chem 1980, 19B: 571-575. Benzisoxazole intermediates used in the preparation of diuretic compounds are described in Chem Pharm Bull 1991, 39(7): 1760-1772. The synthesis of various benzisothiazoles is described in Tetrahedron 1988, 44(10): 2985-2992.